My ex wife was like this, but I didn't get it then, because I was inexperienced when I got with her... When she would give me head, she would really get into it sometimes and would basically 'mouth fuck' me... And when doing that, if she fingered herself for even 20-30 seconds, she would cum like crazy. (where normally, her own masturbation would take a few minutes to get her off)

I loved it, because when she was cumming, she would suck my cock like a demon, often making me cum too.